fix(ui): Track last prompt token count in processStream (#8650)

packages/core/src/core/client.ts

@@ -49,6 +49,7 @@ import {
 import type { IdeContext, File } from '../ide/types.js';
 import { handleFallback } from '../fallback/handler.js';
 import type { RoutingContext } from '../routing/routingStrategy.js';
+import { uiTelemetryService } from '../telemetry/uiTelemetry.js';
 
 export function isThinkingSupported(model: string) {
   return model.startsWith('gemini-2.5') || model === DEFAULT_GEMINI_MODEL_AUTO;
@@ -772,6 +773,8 @@ export class GeminiClient {
       };
     }
 
+    uiTelemetryService.setLastPromptTokenCount(newTokenCount);
+
     logChatCompression(
       this.config,
       makeChatCompressionEvent({